Recently, northern Israel faced what many had been dreading since Iran began its military buildup in Syria: air raid sirens and hours in bomb shelters.

Fortunately, Iran's rocket attack was small enough for Israel's vaunted missile defense system to protect its citizens without casualties. Unfortunately, this may not be the case if Iran or its surrogate Hezbollah choose to attack Israel again in the future.

The Israel Defense Forces', or IDF's, response was limited to missile and artillery attacks against Iranian military targets in Syria. But the international community must understand that, in the future, defending Israel could necessitate major offensive action against enemies that could quickly overwhelm Israel's defenses.

Just last week we participated in a fact-finding mission to Israel, including site visits to Israel's borders with Lebanon and Syria. The IDF understands missile defenses are just one element of its capabilities - air, sea, and ground - that Israel may need to confront this omnipresent threat. Our interactions also reaffirmed the IDF's commitment to the law of armed conflict, especially the significant measures the IDF will take to mitigate risks to civilians, whenever such conflict might come.

IDF operations in that conflict will have to be much larger, faster, and more lethal than the 2014 Gaza or 2006 Lebanon campaigns. In Lebanon, Iran has bolstered the offensive weaponry of its primary proxy Hezbollah by an order of magnitude since the last war with Israel in 2006. Hezbollah now has more than 100,000 rockets and missiles. This expanded arsenal can range all of Israel with much more accurate and powerful warheads than ever before.

With Tehran's help, Hezbollah is also developing its own manufacturing capabilities for precision attack weapons. At the same time, Iran is busy turning Syria into a second front on Israel's borders, even emplacing additional missile batteries targeting Israel. Further complicating the situation, thousands of Hamas rockets remain in Gaza as a potential third front.

How Iran, Hezbollah, and Hamas would employ these weapons compounds the threat. Unlike recent conflicts, the sheer number and improved accuracy of these missiles could likely overwhelm Israel's missile defenses or force it to prioritize protecting military assets. Israeli cities and critical infrastructure would become uniquely vulnerable, thereby eliminating the relative luxury of "strategic patience" that existed in previous conflicts.

Israel may continue its current restrained approach in the face of these threats, but this could create opportunities for Israel's adversaries to launch a massive attack on their own timetable. At that point, Israel will be forced to strike these launch sites and associated military targets through a combined-arms ground operation characterized by speed and shock effect.

While these demands on the IDF in the "next war" likely will be unprecedented, we also understand its primary challenge may not be operational. Knowing they will struggle to defeat Israel militarily, Tehran and its proxies will try to generate international pressure on Israel by exploiting images of civilian casualties and destruction of civilian property. The idea is to paint a picture of a callous and inhumane IDF.

But the truth is, such a conflict would be between a professional military determined to implement extraordinary measures to protect civilians, and illicit enemies determined to expose civilians to risk. Mimicking Hamas in the 2014 Gaza conflict, Hezbollah deliberately shields its tens of thousands of missiles and other military assets in homes, schools, hospitals, and similar sites.

The intent is clear: exploit the presence of civilians as human shields, either to deter Israeli attacks or generate civilian casualties if Israel does strike. Hezbollah knows what Hamas knows: Once the IDF initiates combined-arms operations, these tactics will drive up civilian casualties, and that is how Hamas and Hezbollah hope to delegitimize Israel's conduct by exploiting widespread misunderstandings of the laws of war.

No one should underestimate the capacity of these groups to distort information and images to disingenuously pin the blame for civilian casualties on Israel. Such manipulation is made even more effective when the watching world does not understand the laws of war.

Israel's use of military power in self defense is lawful, yet even a perfect commitment to legal compliance cannot prevent all civilian casualties, especially against an enemy determined to make them happen. It would be wrong to measure Israel's commitment with a facile standard of "casualty counting" that simply equates the effects of combat with their supposed illegality.

Otherwise, the U.S. and its allies can expect similar challenges in their own campaigns against ISIS and other groups that exploit the laws of armed conflict in hopes of achieving in the court of international opinion what they cannot on the battlefield.